computer relearn
Safety Car
Joined: Aug 2009
Posts: 3,745
Likes: 275
From: Melbourne, Victoria, Australia
the ecm will need a little time to relearn and after even ten mins of driving the engine should be running smoothly, the codes are only set when a sensor it monitors is out of specification. The code will tell you what the fault is.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
When you remove power from the ECM it forgets all the BLMs (Block Learn Multipliers) as well as the error codes. The ECM uses the BLMs to compute the injector pulse width, so they affect your AFR.
The ECM sets all the BLMs to a default value when you do a reset and then adjusts them depending on what conditions it sees while you are driving. BLMs are only updated in closed loop mode, so that's why the engine has to be warmed up for learning to take place.
The ECM sets all the BLMs to a default value when you do a reset and then adjusts them depending on what conditions it sees while you are driving. BLMs are only updated in closed loop mode, so that's why the engine has to be warmed up for learning to take place.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Obviously you have to remove power to replace the EPROM, so the answer is yes.
It's not a big deal. When the ECM is in closed loop mode it's always tweaking the BLMs and it only takes a few minutes of driving to get them back where they need to be.
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 411
From: WV
:
My 89 takes about 50 miles before the car is running perfect again..Until then there is always something that's not acting exactly like it should, but corrects gradually as I drive it....Also, right after reconnecting the battery, give the ecm some time to relearn before you start pounding on the engine, the ecm has things to relearn before it's getting the proper A/F again... 
...WW
The BLMs are reset when power is removed from the ECM (they reside in RAM, which is volatile -- meaning that everything goes away when power is removed).
Obviously you have to remove power to replace the EPROM, so the answer is yes.
It's not a big deal. When the ECM is in closed loop mode it's always tweaking the BLMs and it only takes a few minutes of driving to get them back where they need to be.
Obviously you have to remove power to replace the EPROM, so the answer is yes.
It's not a big deal. When the ECM is in closed loop mode it's always tweaking the BLMs and it only takes a few minutes of driving to get them back where they need to be.
My 89 takes about 50 miles before the car is running perfect again..Until then there is always something that's not acting exactly like it should, but corrects gradually as I drive it....Also, right after reconnecting the battery, give the ecm some time to relearn before you start pounding on the engine, the ecm has things to relearn before it's getting the proper A/F again... ...WW
Last edited by WW7; Jun 7, 2014 at 08:00 AM.
Drifting
Joined: May 2013
Posts: 1,736
Likes: 31
From: Reno Nevada
The blm is not used in power enrichment mode in the L98. It defaults to a base fuel maps and adds a percentage based on a PE table and runs about 12:1 afr. Under light load it adjusts to 14.7:1 and saves these settings until power is removed.
